1. Field of the Invention
The present invention relates to an angular velocity sensor using a piezoelectric element.
2. Related Background Art
As angular velocity sensors used for controlling attitudes of moving bodies such as vehicles, typically, ones having various shapes such as an alphabetical H-shaped one, a pillar-shaped one, and a tuning fork-shaped one are known.
These angular velocity sensors are configured from a base, a drive electrode part, and a detection electrode part. Electrode parts for input/output extraction to/from an outside are provided on an upper surface of the base. The electrode parts for input/output extraction are connected with the drive electrode part and the detection electrode part with electrode wires and electrode pads. Each of the electrode parts includes a piezoelectric element having a piezoelectric film. The piezoelectric film sandwiched by an upper electrode and a lower electrode, of the piezoelectric element, has piezoelectric characteristics, and causes distortion when being applied a voltage and causes a potential when mechanically distorted. By use of the characteristics, the piezoelectric element excites the drive electrode part of the angular velocity sensor. When an angular velocity is applied to the angular velocity sensor, the drive electrode part is distorted by Coriolis' force, and a potential is caused in the detection electrode part, accordingly. By detecting of the potential, the angular velocity provided to the angular velocity sensor can be detected. Note that the angular velocity sensor is mounted on a base or the like, then connected with an external circuit by wire bonding or the like, and packaged with an IC that is a processing circuit, thereby to become the angular velocity sensor.
As the piezoelectric element used in such an angular velocity sensor, for example, Patent Document 1 has proposed a piezoelectric element in which a first surface (lower surface) of a piezoelectric body, on which a first electrode (lower electrode) is provided, is formed into a shape having a contour at an outer side than a contour of a second surface (upper surface) of a piezoelectric body, on which a second electrode (upper electrode) is provided, the contour being projected on the first surface (lower surface), the first electrode (lower electrode) is formed into a shape that is the same as or larger than the contour of the first surface (lower surface), and the second electrode (upper electrode) is formed into a shape that is the same as or smaller than the contour of the second surface (upper surface), thereby to effectively prevent a short circuit between the electrodes without increasing resonance performance of the piezoelectric element.
(Patent Document 1) Japanese Patent Application Laid-Open No. 2010-135595 A